Tom Lane wrote:
Richard Huxton <dev@xxxxxxxxxxxx> writes:
Tom - does the planner/executor know it's got row estimates wrong? That
is, if I'm not running an EXPLAIN ANALYSE is there a point at which we
could log "planner estimate for X out by factor of Y"?
Not at the moment, but you could certainly imagine changing the executor
to count rows even without EXPLAIN ANALYZE, and then complain during
plan shutdown.
Not sure how helpful that would be; there would be a lot of noise from
common cases such as executing underneath a LIMIT node.
Hmm - thinking about it you'd probably want to record it similarly to
stats too. It's the fact that the planner *repeatedly* gets an estimate
wrong that's of interest.
Would it be prohibitive to total actions taken - to act as raw data for
random_page_cost / cpu_xxx_cost? If you could get a ratio of estimated
vs actual time vs the various page-fetches/index-fetches etc. we could
actually plug some meaningful numbers in.
--
Richard Huxton
Archonet Ltd
